1. Field of the Invention
The present invention relates to a method of, and an apparatus for drying shaped ceramic bodies having a first surface with an enriched unevenness, and a second surface which is less uneven than said first surface, such as shaped ceramic bodies prepared for manufacturing suspension-type insulators or hollow insulators.
2. Description of Related Art
Heretofore, in order to quickly dry shaped ceramic bodies of a simple configuration, such as a flat plate, there has been typically used an infrared heater. However, such infrared heater is not used for drying shaped ceramic bodies for suspension-type insulators or hollow insulators, having one side which is a complex surface with significant unevenness as compared to its thickness, and an opposite side which is a simple surface with less unevenness as compared to the complex surface. This is because the complex surface of the shaped ceramic body has a large surface area per unit volume and thus receives a higher amount of radiation heat from the infrared heater, whereas the simple surface has a small surface area per unit volume and thus receives a lower amount of radiation heat. This means that the temperature distribution in the shaped ceramic body as a whole becomes non-uniform, and the convex regions in the complex surface are heated to a higher temperature than the concave regions so that so-called "drying cracks" tend to be formed in the convex regions.
In view of the above-mentioned drawbacks, it has been a conventional practice to dry shaped ceramic bodies of complex configuration by means of hot wind re-circulation process, such as environmental drying process, or a natural drying process. However, such a drying process requires substantial drying time, ranging from several tens to several hundreds hours, besides that the drying state becomes unstable due to environmental influences and is not easy to control.